Pulsating electric discharge



Nov. 22, 1960 c. KENTY PULSATING ELECTRIC DISCHARGE Filed 001;. 2, 195aInventor Carl, k'ervt b5 5 His A t tovneg.

United States PatentO PULSATING ELECTRIC DISCHARGE Carl Kenty, ClevelandHeights, Ohio, assignor to General Electric Company, a corporation ofNew York Filed Oct. 2, 1958, Ser. No. 764,812

Claims. (Cl. 313-174) This invention relates to a pulsating discharge ina mixture of mercury vapor and neon.

I have discovered that under certain circumstances pulsations occur inthe positive column of a discharge in mercury vapor with neon. Thephenomenon may appear as a red wave travelling along an otherwise bluedischarge. The general object of the invention is to provide novelelectric discharge devices exhibiting this phenomenon.

The pulsing phenomenon occurs in mixtures of mercury vapor inequilibrium with condensed mercury at a temperature in the range from 20to 40 C., with neon gas at a pressure in the range from approximately 1to 3 millimeters. The range of currents wherein it occurs is fromapproximately 0.2 to 3.5 amperes in tubes ranging from approximately to35 millimeters in internal diameter.

Other objects and advantages of the invention will appear in thefollowing detailed description of representative embodiments read inconjunction with the accompanying drawing. The features of inventionbelieved to be novel will be more particularly pointed out in theappended claims.

In the drawing:

Fig. 1 illustrates in side view a discharge lamp embodying the inventionin conjunction with an operating circuit therefor schematicallyillustrated.

Figs. 2a and 2b illustrate in side and end views another discharge lampembodying the invention with a simplified mercury vapor pressure controlarrangement.

Fig. 3 illustrates another mercury vapor pressure control means whichmay be used with the lamp of Fig. 1.

Referring to Fig. 1 the invention is embodied in an elongated vitreoustube 1 having enlarged chambers 2, 2' at opposite ends in which aresealed the electrodes 3, 3'. Each electrode comprises a tungstenfilament 4 activated by the usual coating of alkaline earth oxides andsupported on inleads 5 sealed through the press 6 of a mount 7. The tubeis devoid of any internal phosphor coating.

The lamp is operated by a ballast autotransformer 8 comprising a primarywinding 9 energized from the usual 115-120 volt A.C. supply at terminals10, and a high reactance secondary win-ding 11 connected in seriestherewith. The electrodes are continuously heated by means of auxiliarywindings 12.

The envelope has a filling of mercury exceeding the quantity vaporizedduring the operation of the lamp, and neon gas in the range fromapproximately 1 to 3 mm. of mercury. The mercury vapor is maintained inequilibrium with the excess 13 thereof which condenses in a tubularextension or appendix 14 extending normally to the envelope 1 near itsmidpoint. In other words the envelope is filled with mercury vapor atthe temperature of saturation T determined by the coolest point of theenvelope, such being the appendix 14. In order to maintain the appendixat the predetermined temperature, it

may be immersed in a water bath 15 contained in a double-walled thermostype bottle 16.

By way of example, in the illustrated embodiment of the invention,vitreous tube 1 has an outer diameter of 15 mm., an internal diameter of13 mm., and a length of approximately 2 feet measured to the shoulder ofthe expanded end chambers 2, 2'. The autotransformer 8 has an opencircuit voltage of approximately 500 volts and provides through the lampa discharge current of approximately 300 milliamperes. With a neonpressure of approximately 2 mm. and a saturation temperature T asdetermined by the temperature of the water bath 15 of 35 C. to 40 C.,the pulsating effect in accordance with the invention is stronglypresent.

The pulsation effect is observed as a wave of red light, illustrated bythe vertical hatching at 17; the wave travels along an otherwise bluepositive column in Hg+Ne, illustrated by the broken horizontal hatchingthroughout the tube. The wave may travel in the direction indicated bythe arrow 18 and is repeated at regular intervals. The red regionappears to be of substantially zero Hg density. It is believed that theHg is cleaned up on the wall in the blue stage of the discharge only tobe released again in the red stage.

The salient features of the pulsation phenomenon are as follows:

The pulsation has been found in mixtures of mercury with Ne but not withHe, Ar, Kr or Xe.

It has been observed with Ne pressures in the range from approximately 1mm. to 3 mm.; with Hg appendix temperatures (T in the range fromapproximately 20 to 40 C.; with tube diameters ranging fromapproximately 10 to 35 mm. (I.D.); with current from approximately 0.2to 3.5 amperes, and with AC. or DC.

The pulsation occurs very well with pyrex or lime glass walls, less wellwith lead glass and apparently not at all with walls coated with afluorescent lamp phosphor.

Pulse frequencies of 3 to 60 per minute have been observed. Thefrequency increases with current and with wall temperature; a steadydischarge in a lead glass tube was made to pulsate by heatingthe wallexternally. The pulse rate increases with decreasing Ne pressure, withdecreasing T and with decreasing tube diameter.

The current range for pulsing increases with increasing Hg appendixtemperature.

The range of T for pulsing increases with decreasing tube diameter.

Beyond the range of pulsing, the discharge is either all blue, e.g., forcurrents too low for pulsing, or has a steady red core, -e.g., forcurrents too large for pulsing (in the latter case the red core beingdue to radial electrophoresis).

When a discharge is started, some minutes must be allowed for the wallsto reach a suitable stage of mercury saturation before pulsing willcommence. During this initial stage, the discharge will be essentiallyred, Hg cleaning up on the wall nearly as fast as it diffuses in fromthe appendix or reservoir. Gradually the discharge turns blue and thenpulsing may commence. Once a pulse pattern has been established, it isvery regular and continues for days or indefinitely if conditions remainconstant. But with different tubes and different condition-s, a widevariety of pulse patterns have been observed. For example, to mentiononly two, the red region may develop in the center of the tube andtravel as two waves toward both ends; or it may appear at one end andtravel toward the other. The direction of the wave appears not to bedetermined by the direction of current in a DC. discharge; however, itwould seem that electrophoresis has some influence on the precisebehavior of the pulsation.

Sometimes a slow secondary pattern is superposed-0n the fundamental modeof pulsation, e.g., the waves may slowly increase toward a maximum andthen die away again and so on.

Observing with a spectroscope, the red Ne lines are strong in the redregion and weak or absent when the discharge is at its bluest. The Hglines do not appear to change nearly as much in strength through thecycle as do the Ne lines. The phenomenon is most striking as seenthrough a red filter glass.

The voltage gradient in the red region has been found with floatingprobes to be to 100% greater than that in the blue stage, depending oncurrent and appendix temperature T Thus when the red wave is at itsmaximum, the discharge voltage may exceed by 10% or more the voltage inthe bluest stage, depending on the extent of the red region;concurrently, depending on the degree of ballasting, the current will belower. The greater the ballasting, and therefore, the more constant thecurrent, the more pronounced the pulsing is, because as above noted, adecrease in current tends to make a red discharge go blue.

If the current is suddenly increased by external means, a blue dischargewill go red, sometimes only for a short time, depending oncircumstances; likewise if the current is suddenly decreased, a red tubeor region will go blue, sometimes only temporarily.

By introducing a periodic variation in the ballast, pulsing has beeninduced in an otherwise steady discharge. The effect is greatest at acertain resonance frequency as might be expected. Under thesecircumstances, the travelling wave nature of the pulse is somewhatsubdued, the whole tube swinging more or less from blue to red and back.There is a noticeable time lag between the current and the visualeffects.

Indications are that the electron temperature T roughly doubles as thedischarge goes from blue to red.

The foregoing observations of pulsing appear to indicate that Hg ionsare cleaned up on the wall during the blue stage and there remain,possibly as neutral atoms, until they evaporate naturally or until theyare knocked off by the impacts of Hg ions or by Ne ions in the redstage. It would seem that Ne ions are particularly effec tive indislodging cleaned-up Hg. It is possible that metastable Ne atoms assistin this process. Further additional heating of the wall during the redstage doubtless assists the evaporation. To account for pulsing, a delaymechanism seems necessary and this could be the natural lifetime of thecleaned-up Hg on the wall, the heating of the wall by the Ne discharge,and the ditfusion time of the Hg vapor in getting back into the body ofthe tube.

A pulsating mercury neon lamp in accordance with the invention lendsitself well to novelty lighting effects. Its usefulness for advertisingpurposes is, of course, apparent. The pulsating effect is most strikingwhen the blue glow from the mercury discharge is cut out and this mayreadily be accomplished by mounting the lamp behind a red glass orplastic sheet in a display window or advertising device. Alternatively,the envelope of the tube may be made of red glass which cuts out theblue light from the mercury and transmits the pulsing red light from theneon discharge. The lamp may of course be formed to any desired shape,for instance to a rectangular or circular outline for an advertisingsign, or else as letter characters or symbols in accordance withadvertising sign practice.

By suitable choice of the design parameters, namely the inside diameterof the tube, the neon pressure and the discharge current, the saturationtemperature T of the mercury at which pulsations occur may be made tocoincide with a given room temperature. In such case the appendix 1-4 isno longer needed and the lamp will pulsate so long as the roomtemperature is held at the selected value. This may not always bepractical to do but other means of maintaining a constant saturationtemperature T are available. For instance as illustrated in Figs. 2a and2b, a small metal radiator comprising several fan-shaped radiating finsfastened to a-curved foot 21 which is held against the body of the lampenvelope 1 by means of a spring 22, may be used to provide a cool spoton the envelope wall. The excess mercury 13' will condense thereat asshown in Fig. 2b, the temperature of this cool spot determining thesaturation temperature T The size or eifectiveness of the radiator maybe varied by swinging out the fins or sectors 20. Thus compensation maybe effected for various room temperatures in order to achieve thedesired saturation temperature T for pulsation.

Fig. 3 shows an alternative arrangement for obtaining a constantsaturation temperature T despite a variable room temperature. Anappendix 14, similar to that illustrated in Fig. l, is provided with athermostatically controlled electric heater. The heater may take theform of several turns of resistance wire 23 wrapped around the appendixand connected in series with the lamp discharge circuit; a thermostaticswitch 24 short circuits the heater winding at the desired temperatureto cut out the heating effect. The heater, switch and appendix arepreferably enclosed in an insulating casing to maintain all parts at thesame temperature.

While certain specific embodiments of the invention have beenillustrated and described in detail, these are intended as exemplary andnot as limitative of the invention whose scope is to be determined bythe appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric discharge device for producing a pulsating red dischargecomprising an elongated vitreous envelope having a pair of electrodessealed into the ends thereof, said envelope containing an excess ofmercury and neon gas at a pressure in the range from approximately 1 to3 millimeters, said envelope having an internal diameter in the rangefrom approximately 10 to 35 millimeters, and means for maintaining themercury in said envelope at a pressure corresponding to a mercurysaturation temperature in the range from 20 to 40 C. whereby a pulsatingred discharge occurs in said envelope upon current flow therethrough inthe range from 0.2 to 3.5 amperes.

2. An electric discharge device for producing a pulsating red dischargecomprising an elongated vitreous envelope having a pair of electrodessealed into the ends thereof, said envelope containing mercury in excessof the quantity vaporized at the saturation temperature in the coolestpart of the envelope and neon gas at a pressure in the range fromapproximately 1 to 3 millimeters, said envelope having an internaldiameter in the range from approximately 10 to 35 millimeters, and meansfor maintaining the coolest part of said envelope at a temperature inthe range from 20 to 40 C. whereby a pulsating red discharge occurs insaid envelope upon current flow therethrough in the range from 0.2 to3.5 amperes.

3.An electric discharge device for producing a pulsating red dischargecomprising an elongated vitreous envelope having a pair of electrodessealed into the ends thereof, said envelope containing mercury in excessof the quantity vaporized at the saturation temperature in the coolestpart of the envelope provided by a laterally projecting appendix andneon gas at a pressure of approximately 2 millimeters, said envelopehaving an internal diameter of approximately 13 millimeters, and

means for maintaining said appendix at a temperature from approximately35 to 40 C. whereby a pulsating red discharge occurs in said envelopeupon passage of a current therethrough of approximately 300milliamperes.

4. The method of producing a pulsating red discharge in an electricdischarge device in the form of an elongated vitreous envelope having apair of electrodes sealed into its ends and containing an excess ofmercury and neon gas at a pressure in the range from approximately 1 to3 millimeters and having an internal diameter in the range fromapproximately 10 to 35 millimeters, which comprises maintaining themercury in said envelope at a pressure corresponding to a mercurysaturation temperature in the range from 20 to 40 C., and adjusting thecurrent flow through said device in the range from 0.2 to 3.5 amperes toobtain the desired pulsating discharge.

5. The method of producing a pulsating red discharge in an electricdischarge device in the form of an elongated vitreous envelope having apair of electrodes sealed into its ends and containing an excess ofmercury and neon gas at a pressure of approximately 2 millimeters andhaving an internal diameter of approximately 13 millimeters, whichcomprises maintaining the mercury in said envelope at a pressurecorresponding to a mer- 15 2,191,507

References Cited in the file of this patent UNITED STATES PATENTS1,876,083 Spaeth Sept. 6, 1932 1,908,647 Spaeth May 9, 1933 2,009,201Pirani et a1. July 23, 1935 2,056,464 Jones Oct. 6, 1936 2,103,039Pirani et a]. Dec. 21, 1937 Spanner Feb. 27, 1940

